1. Field of the Invention
The present invention relates to a precision balance of the type having a short-stroke measuring system and a load receptor connected to the measuring system by means of a hanger.
2. Description of the Related Art
In high-resolution precision balances, even a slight shock to the weighing pan when loading a weighing object on the weighing pan can lead to damage in sensitive components of the balance. Such damage arises as a consequence not only of an overload or an eccentric load acting in the direction perpendicular to the pan, but also from forces that are introduced into the hanger transversely of or at an acute angle relative to the weighing pan.
From the prior art, precision balances are known in which the hanger is protected from damage by means of an overload or eccentric load protection device.
In Swiss Patent Nr. 576,634, the weighing pan of the balance is constructed in two parts. The pan which receives the weighing object rests on an under-pan of light sheet metal, wherein the under-pan has an annular rim which ends only a few millimeters from the enclosure of the balance. Concentric with the rim, in a hole with loose play, a hollow bolt is inserted, the bolt having a collar that bears loosely against the under-pan. A retaining ring is fitted on the leg of the hollow bolt. Held captive between the retaining ring and the under-pan, there is, in addition, a star-shaped leaf spring which, with the tips of its arms, presses the under-pan against the collar of the bolt. The star-shaped spring is prestressed to an extent that the spring force bearing against the under-pan is greater than the maximum weighing load of the precision balance. Consequently, when weighing within the weighing range of the balance, the under-pan remains held in contact with the collar, and the spring has no influence on the weighing force. If an eccentric load acts on the weighing pan, particularly if the load exceeds the weighing range of the balance, the weighing pan will be allowed to tip on the side of the load, and the under-pan will come to rest against the enclosure of the balance. Damage to mechanical elements, e.g., to the parallel-motion linkage, guide arms, etc. is thus prevented.
This known device meets its purpose as long as the excessive load acts on the weighing pan essentially vertically from above. A force acting horizontally or from an acute angle will not be absorbed by the spring-loaded support of the weighing pan, but will impact directly on the hanger.
A device protecting against eccentric load/overload operating in a similar manner is also disclosed in U.S. Pat. No. 4,475,898 and in DE-C2-3242156. In these known balances, too, forces meeting the weighing pan horizontally or at an angle are not kept from reaching the hanger.